Re: [PATCH v1] arm64: dts: qcom: hamoa-iot-evk: support Bluetooth over both USB and UART

[Shuai Zhang <shuai.zhang@oss.qualcomm.com>]

Hi Konrad

On 3/11/2026 9:07 PM, Konrad Dybcio wrote:
> On 3/11/26 10:09 AM, Shuai Zhang wrote:
>> When Bluetooth supports both USB and UART, the BT UART driver is
>> always loaded, while USB is hot-pluggable. As a result, when Bluetooth
>> is used over USB, the UART driver still be probed and drive BT_EN low,
>> which causes the Bluetooth device on USB to be disconnected.
> Is bluetooth connected over UART *and* USB simultaneously?
BT uses either UART or USB, never both at the same time.

On platforms supporting both, the UART driver is always probed, while 
USB is hot‑pluggable.

As a result, when BT runs over USB, the UART driver still probes and 
pulls BT_EN low,

unintentionally powering off the USB BT device.

>
>> Configure BT_EN as a GPIO hog so that it is controlled by the platform
> What's "the platform"?

hamoa-evk


>
>> instead of the UART driver, preventing BT over USB from being
>> unintentionally powered down.
>>
>> Signed-off-by: Shuai Zhang <shuai.zhang@oss.qualcomm.com>
>> ---
>>   arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts b/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts
>> index 630642baa435..60a0b3ecbc1b 100644
>> --- a/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts
>> +++ b/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts
>> @@ -647,10 +647,9 @@ wcn7850-pmu {
>>   		vddrfa1p2-supply = <&vreg_wcn_1p9>;
>>   		vddrfa1p8-supply = <&vreg_wcn_1p9>;
>>   
>> -		bt-enable-gpios = <&tlmm 116 GPIO_ACTIVE_HIGH>;
> What if I want to power down Bluetooth now?


It cannot be pulled low because it is not possible to determine whether 
the inserted M.2 card is UART‑based or USB‑based.

Identifying whether the interface is USB or UART would allow control of 
the UART probe accordingly;

however, no reliable solution is available so far. Additional approaches 
are still being explored.


>
>>   		wlan-enable-gpios = <&tlmm 117 GPIO_ACTIVE_HIGH>;
>>   
>> -		pinctrl-0 = <&wcn_bt_en>, <&wcn_wlan_en>;
>> +		pinctrl-0 = <&wcn_wlan_en>;
>>   		pinctrl-names = "default";
>>   
>>   		regulators {
>> @@ -1398,11 +1397,12 @@ wcd_default: wcd-reset-n-active-state {
>>   		output-low;
>>   	};
>>   
>> -	wcn_bt_en: wcn-bt-en-state {
>> -		pins = "gpio116";
>> -		function = "gpio";
>> -		drive-strength = <2>;
>> -		bias-disable;
>> +	wcn_bt_en_hog: wcn-bt-en-state-hog {
> This name is illegal (make CHECK_DTBS=1 qcom/hamoa-iot-evk.dtb)


|I will use tlmm to control|


>
>> +		gpio-hog;
>> +		gpios = <116 GPIO_ACTIVE_HIGH>;
>> +		output-high;
>> +		input-disable;
> This property is not allowed for TLMM pins
>
>> +		link-name = "BT_EN";
> This property doesn't exist


I  will remove it;


>
> Konrad


thanks,
Shuai